Vehicle barrier systems are commonly used for preventing the passage of a vehicle or traffic along a vehicle pathway, such as a road or driveway. Signal barriers such as gate arms act as signalers, instructing the vehicle driver to halt and await clearance before proceeding through a checkpoint area. Signal barriers are limited in effectiveness, however, insofar as a moving vehicle can crash through the gate arm without disabling the vehicle. Hence, signal barriers do not physically restrict access to an area, but generally merely act as warning devices and deterrents.
Vehicle barrier systems that function as barricades are disclosed in, for example, U.S. Pat. Nos. 5,466,088, 4,574,523 and 4,630,395. These barricades are low lying in the roadway and moveable from a generally horizontal position to an angularly disposed position for blocking the passage of a vehicle along the roadway. The barricades may be used alone or in combination with a signal barrier, such as a gate arm, as shown in U.S. Pat. No. 5,466,088. An advantage to the use of barricades over signal barriers is that the barricades are constructed to absorb the impact force created by the collision of a vehicle therewith, thereby preventing the progress of the vehicle past the barricade. Barricades are especially effective as both deterrents and impediments against terrorists and other hostile individuals intent on transporting a vehicle carrying armed personnel or explosives next to or into a building, e.g., for the purpose of permitting the personnel to swiftly infiltrate the building or detonating the explosives with optimal destructive effect to the building and its occupants. As a consequence, barricades have become common defensive equipment at such facilities as oil refineries, satellite communication stations, embassies, military bases, and other government installations.
The vehicle barrier systems disclosed in the aforementioned patents generally feature a barricade operated by a controller to move between open and closed positions. In the open position, the barrier is lowered so as not to impede the passage of vehicle traffic along a vehicle passageway, such as a road, thoroughfare, private access way, driveway, etc. In the closed position, the barrier is raised to physically obstruct vehicle movement.
The barrier systems include an actuator system connected to the barricade for moving the barricade between its open and closed positions. The actuator system typically features hydraulics, such as a piston and rod assembly, for raising and lowering the barricade. A motor drives the actuator to move the barricade between the open and closed positions. The motor is operatively connected to a barrier controller, which controls operation of the barrier and is operated automatically or manually, such as by a security guard or other authorized personnel. Oftentimes the barricade is retained in its closed, raised position until such time as vehicle occupants seeking to traverse the barricade present proper identification or authorization to proceed. The security guard will then activate the barrier controller to lower the barricade. Alternatively, in high traffic areas and the like, the security guard may retain a barricade in its open, lowered position until such time as the guard perceives an imminent threat, such as a hostile vehicle approaching the barricade at high speed without manifesting an intention to stop at the checkpoint.
Generally, the girth and massive weight of vehicle barricades are responsible for the relatively slow rates at which barricades can be raised from their open position to their closed position. Accordingly, a security guard must be vigilant in observing for hostile behavior so as to act to raise the barrier before a hostile vehicle may traverse the lowered barricade. A moment of inattention or distraction can in some cases afford enough of a time window to permit the hostile vehicle to bypass the security barricade before it is raised to a sufficient height to obstruct passage.
It is known to equip a hydraulic actuator system with an accumulator to permit the barricade to be raised at a faster than normal operation rate for emergency situations. An alternating current electric power source is used to operate a pump and cause pressurized hydraulic fluid to store in the accumulator. Upon activation of an emergency switch, the stored pressurized hydraulic fluid is charged from the accumulator into the hydraulic actuator, which raises the barricade into the closed position at a faster than normal operation rate, before an unauthorized vehicle can traverse the barrier system.
Although hydraulic accumulators generally are adequate for raising the barrier in emergency situations, if not operated and maintained properly accumulators can malfunction or function at less than optimum levels. For example, improper maintenance or use, such as in the case of a foreign object becoming trapped in and obstructing the movement of the barrier mechanical system, can generate back pressure in the hydraulic system and compromise pressure seals of the hydraulic accumulator. Further, disruption of electric power to the barrier system, for example in the case of a power failure or an attack by a terrorist on a supplying power source, can deleteriously affect the normal and emergency operations of the barricade.